What would happen to Nuclear Power Stations if…
Discussion
Gary C said:
So at some point the reactors would trip. Lots of reasons for that to happen from faults to blocking coolers.
Rods would go in and the automated cooling systems would cool the reactor down.
What happens next depends.
Lets say its the grid that takes it off (as stations trip, the grid would collapse with the same result) and then the stations would be on backup generation. Each station has a lot of fuel to run the backups, but their design mission time is about 24 hours and even thought they can last much longer, they also assume that some equipment is shutdown as the requirements for cooling reduce. With no people, all systems would continue to run using more fuel than anticipated.
Haven't worked it out (its written down somewhere), but eventually the backup generators would stop and the cooling systems would shutdown.
Now, a reactor thats been shutdown for, lets say 7 days, is still producing about 5-10MW of heat and will begin to warm up. Eventually in theory some reactors can go critical again if they warm up enough and that would mean a meltdown.
Big cores such as AGR's heat quite slowly but have a positive moderator coefficient whereas most water reactors have a much smaller core and thus heat up quicker but have a self regulating negative moderator coefficient.
If everything works ok, its likely that even when the generator fuel runs out, the remaining decay heat won't be enough to melt the reactor down but I wouldnt like to try it.
I know that beyond design basis studies have looked at the effects, but its not something that Operators generally look at in simulator exercised.
surprised the backup genny aren’t designed or have enough fuel to ensure that it can be completely shutdown to cold (how long is that even)Rods would go in and the automated cooling systems would cool the reactor down.
What happens next depends.
Lets say its the grid that takes it off (as stations trip, the grid would collapse with the same result) and then the stations would be on backup generation. Each station has a lot of fuel to run the backups, but their design mission time is about 24 hours and even thought they can last much longer, they also assume that some equipment is shutdown as the requirements for cooling reduce. With no people, all systems would continue to run using more fuel than anticipated.
Haven't worked it out (its written down somewhere), but eventually the backup generators would stop and the cooling systems would shutdown.
Now, a reactor thats been shutdown for, lets say 7 days, is still producing about 5-10MW of heat and will begin to warm up. Eventually in theory some reactors can go critical again if they warm up enough and that would mean a meltdown.
Big cores such as AGR's heat quite slowly but have a positive moderator coefficient whereas most water reactors have a much smaller core and thus heat up quicker but have a self regulating negative moderator coefficient.
If everything works ok, its likely that even when the generator fuel runs out, the remaining decay heat won't be enough to melt the reactor down but I wouldnt like to try it.
I know that beyond design basis studies have looked at the effects, but its not something that Operators generally look at in simulator exercised.
Edited by Gary C on Saturday 29th January 06:24
Is there an assumption that the grid would come back within 24hrs to run the house loads?
eliot said:
surprised the backup genny aren’t designed or have enough fuel to ensure that it can be completely shutdown to cold (how long is that even)
Is there an assumption that the grid would come back within 24hrs to run the house loads?
Presumably the assumption is that someone would refuel the generators.Is there an assumption that the grid would come back within 24hrs to run the house loads?
I guess if a large % of the population vanished then many things like the reactor would just stop working. I suppose all that infrastructure would simply grind to a halt and there would be piles of things just sitting where they were when the human interacting with it disappeared.
Most of the ‘things’ we use that kind of define our society need fuel don’t they really. Would power and phone signals or the internet all keep working if the people monitoring it or running it vanished?
Something like an aircraft would just crash if it was being hand flown or if the autopilot was on it would go to the destination that had been programmed and likely take up a holding pattern and do that until the fuel ran out and then fall from the sky over or near the destination airport. Sucks if the 10% that didn’t vanish were on the plane and didn’t know what to do.
I suppose a car would just decelerate and do it’s thing and come to a stop by likely hitting something.
There would likely be a lot of vehicles in the sky sea and ground initially doing their own thing for a bit but all run on some kind of fuel.
If most people vanished I expect there would still be widespread chaos as people would panic and there would be hardly any police or government or people to transmit their instructions or assure them etc. plus the survivors would rightly be concerned about what happened to everyone else and what was going to happen next.
Then people would naturally form into groups and new ways to organise ourselves would grow up and we’d eventually be back to something like we have now after a few decades perhaps but with less people.
It would be interesting seeing if the survivors could restart many of these things or processes with little knowledge and what parts of our old society and culture just never got replaced.
Maybe we could all view this scenario from our own jobs perspective and say what would happen to society if we vanished whilst at work or doing what we’re needed for?
If I was flying an aircraft and the pilots vanished then depending on what part of the flight it was and what we’d programmed into the flight management computer, it would likely continue to the destination take up the hold and circle until the fuel ran out then it would crash into the ground. If we were hand flying it and vanished then it would crash a lot sooner.
I suppose if my wife and kids didn’t vanish then they’d survive but obviously if my whole family vanished then our animals/pets might not last long as they’d likely be in the house still.
Most of the ‘things’ we use that kind of define our society need fuel don’t they really. Would power and phone signals or the internet all keep working if the people monitoring it or running it vanished?
Something like an aircraft would just crash if it was being hand flown or if the autopilot was on it would go to the destination that had been programmed and likely take up a holding pattern and do that until the fuel ran out and then fall from the sky over or near the destination airport. Sucks if the 10% that didn’t vanish were on the plane and didn’t know what to do.
I suppose a car would just decelerate and do it’s thing and come to a stop by likely hitting something.
There would likely be a lot of vehicles in the sky sea and ground initially doing their own thing for a bit but all run on some kind of fuel.
If most people vanished I expect there would still be widespread chaos as people would panic and there would be hardly any police or government or people to transmit their instructions or assure them etc. plus the survivors would rightly be concerned about what happened to everyone else and what was going to happen next.
Then people would naturally form into groups and new ways to organise ourselves would grow up and we’d eventually be back to something like we have now after a few decades perhaps but with less people.
It would be interesting seeing if the survivors could restart many of these things or processes with little knowledge and what parts of our old society and culture just never got replaced.
Maybe we could all view this scenario from our own jobs perspective and say what would happen to society if we vanished whilst at work or doing what we’re needed for?
If I was flying an aircraft and the pilots vanished then depending on what part of the flight it was and what we’d programmed into the flight management computer, it would likely continue to the destination take up the hold and circle until the fuel ran out then it would crash into the ground. If we were hand flying it and vanished then it would crash a lot sooner.
I suppose if my wife and kids didn’t vanish then they’d survive but obviously if my whole family vanished then our animals/pets might not last long as they’d likely be in the house still.
Edited by anonymous-user on Saturday 29th January 07:53
mike74 said:
Well I'd prefer it if 100% of the planet destroying parasites were wiped out overnight and the natural world was left to recover from the current Anthropocene mass extinction.
What use is a paradise earth if we’re not here to enjoy it?There’ll be billions of unspoiled planets around the universe, do you get a warm glow thinking about them?
How very thought provoking
charltjr said:
The reactors would shut themselves down in the event of a problem - unless someone had done something truly stupid like disabling the safety systems.
Chernobyl wouldn’t have happened if the safety systems hadn’t been manually disabled so that the operators could try and force through a safety check. Irony…..
Freeman Dyson once said that designing a reactor to be idiot proof was easy, designing one to be physicist proof was the difficult bit Chernobyl wouldn’t have happened if the safety systems hadn’t been manually disabled so that the operators could try and force through a safety check. Irony…..
Bill said:
Also amused at the OP's use of "unlikely" to describe 99.9% of the population just vanishing. 
It’s like when your kids keep asking “but what if” (whatever disaster scenario) DID happen . . . it usually ends with death or something suboptimal.
I was in a meeting at work where we were asked about designing a procedure to follow if someone hit us with a surface to air missile (when that sort of thing was more in vogue)
Unfortunately the first thing I could come up with was that we’d take it up the bum like a good ‘un.
After some snorts and then silence, it was reluctantly agreed as being the most likely outcome and we moved on to discussing pay or something.
LaurasOtherHalf said:
mike74 said:
Well I'd prefer it if 100% of the planet destroying parasites were wiped out overnight and the natural world was left to recover from the current Anthropocene mass extinction.
What use is a paradise earth if we’re not here to enjoy it?There’ll be billions of unspoiled planets around the universe, do you get a warm glow thinking about them?
How very thought provoking
Then the arriving aliens or next dominant species to evolve would look at it all and think WTF.
El stovey said:
The world wouldn’t recover it would still have all our stuff everywhere like some gyppo site or an overgrown council garden.
Then the arriving aliens or next dominant species to evolve would look at it all and think WTF.
Of course the earth would recover and thrive on a geological timescale and without any other species becoming dominant (yet also stupid) enough to destroy their own environment. Then the arriving aliens or next dominant species to evolve would look at it all and think WTF.
(Although I agree it would look a bit of s
t tip to begin with!)Mr Pointy said:
It takes more than a few hundred people just to service the wind farms we have now, let alone the thousands needed to keep the distribution system going.
At current capacity/output, yes. But a network supplying 60k people, probably less if they only focus on population centres, should require less resource to maintain.Likely that rural areas would not be served and services were focussed on a few towns.
Likely no great demands for power either. Large scale manufacturing would stop, large retail parks, shopping centres, offices, warehouses etc all closed.
mike74 said:
I think a few nuclear power stations going bang would be a small price to pay for the overall gains the planet would benefit from by 99.9% of the human population disappearing over night... some minor short term pain for long term gain.
Quite agree. The older I get the more I've realised that we as a race really do have very little to offer, we're stupid, self interested, we keep repeating the same mistakes and are willing to do really horrific stuff to our fellow man/the environment in order to line our pockets or in the name of religion or nationalism.The world can and has recovered from amazing things, check out how quickly it recovered following the P-T extinction event of 250 million ago, only 3-10 million years.
eliot said:
surprised the backup genny aren’t designed or have enough fuel to ensure that it can be completely shutdown to cold (how long is that even)
Is there an assumption that the grid would come back within 24hrs to run the house loads?
When is cold ?Is there an assumption that the grid would come back within 24hrs to run the house loads?
Decay heat doesn't go away (well, it does but only increasingly slowly)
But if you mean to insignificant fission product heating, then its assumed that external supplies or either fuel or electricity will be available. I think we postulated 24 hours so were designed for 48 hours, but recently our minimum stocks on diesel fuel were increased to ensure we could last significantly longer after Fukushima and other analysis.
Certainly even after 12 days, one of our reactors is still producing about 3.5MW of heat and that reactor wasn't shutdown from full power so its lower than it normally would have been.
But, on trip, every bit of kit and every diesel engine stars and its assumed that after the initial cooling and reduction of decay heat, the operators will shutdown loads that are no longer needed, reducing load on the backup generators.
LaurasOtherHalf said:
mike74 said:
Well I'd prefer it if 100% of the planet destroying parasites were wiped out overnight and the natural world was left to recover from the current Anthropocene mass extinction.
What use is a paradise earth if we’re not here to enjoy it?There’ll be billions of unspoiled planets around the universe, do you get a warm glow thinking about them?
How very thought provoking
‘So you’d like everybody in the world destroyed?’ said Ursula.
‘I should indeed.’
‘And the world empty of people?’
‘Yes truly. You yourself, don’t you find it a beautiful clean thought, a world empty of people, just uninterrupted grass, and a hare sitting up?’
The pleasant sincerity of his voice made Ursula pause to consider her own proposition. And really it was attractive: a clean, lovely, humanless world. It was the really desirable. Her heart hesitated, and exulted. But still, she was dissatisfied with him.
‘But,’ she objected, ‘you’d be dead yourself, so what good would it do you?’
‘I would die like a shot, to know that the earth would really be cleaned of all the people. It is the most beautiful and freeing thought. Then there would never be another foul humanity created, for a universal defilement.’
‘No,’ said Ursula, ‘there would be nothing.’
‘What! Nothing? Just because humanity was wiped out? You flatter yourself. There’d be everything.’
‘But how, if there were no people?’
‘Do you think that creation depends on man! It merely doesn’t. There are the trees and the grass and birds. I much prefer to think of the lark rising up in the morning upon a human-less world. Man is a mistake, he must go. There is the grass, and hares and adders, and the unseen hosts, actual angels that go about freely when a dirty humanity doesn’t interrupt them–and good pure-tissued demons: very nice.’
You might find this essay interesting:
https://catherinebrown.org/describing-the-unobserv...
105.4 said:
Gary, thank you very much for that 
Just one more question if I may….
What is / are positive & negative moderator coefficients?
Right, bear with meJust one more question if I may….
What is / are positive & negative moderator coefficients?
Fission releases very fast neutrons that have to be slowed down enough to have enough of a chance of fissioning another atom of fuel.
The moderator slows down the neutrons
The moderator has a certain 'efficiency' of doing its job. If it gets worse, the number of 'slow' neutrons reduces, the amount of fission reduces and power goes down. If the moderator gets better the reverse happens
The rods absorb neutrons, the more they insert, the more they absorb, the lower the power. If they absorb enough, the reactor will be shutdown.
But they dont absorb every neutron
If the moderator efficiency increases enough, it is possible that it can moderate enough of the neutrons not mopped up by the control rods and the reactor will go critical (and actually supercritical) and power can increase.
El stovey said:
Then people would naturally form into groups and new ways to organise ourselves would grow up and we’d eventually be back to something like we have now after a few decades perhaps but with less people.
It would be interesting seeing if the survivors could restart many of these things or processes with little knowledge and what parts of our old society and culture just never got replaced.
One thing that's got people concerned is how much of our information is stored only digitally, with no hard copy - something such as the Carrington event / solar flare referenced above might leave us without the technical instructions to use and rebuild what we already have.It would be interesting seeing if the survivors could restart many of these things or processes with little knowledge and what parts of our old society and culture just never got replaced.
eliot said:
surprised the backup genny aren’t designed or have enough fuel to ensure that it can be completely shutdown to cold (how long is that even)
Is there an assumption that the grid would come back within 24hrs to run the house loads?
Have a little google for Hunterston B incident December 1998.Is there an assumption that the grid would come back within 24hrs to run the house loads?
It all went to s
t and was without cooling for 4 hours…according to Wikipedia it could have lasted another 20.So 24 hours with no cooling.
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